1. Field of the Invention
The present invention demonstrates the method applied is a new one comprising butt-couple and prism-couple together with phase-modulation method.
For the integrated optical-components, such as modulator, directional coupler, switcher, and wave-length division multiplexer, the basic structure is a waveguide. Consequently, the characteristics of waveguides remain an important area of study for the integrated optical-components. Among which, the most critical one is the propagation loss. The reason being that the value can be used for improving the manufacturing process of integrated optical-components as well as evaluate their functions.
2. Description of the Prior Art
As of present, the customary technologies in practice for measuring the propagation loss are only applicable to single mode waveguide. Besides, such technologies are only able to measures the total propagation loss of multi-mode waveguide, and not capable of distinguishing the individual propagation loss of every individual mode for a multi-mode waveguide. Moreover, among the integrated optical-components built by waveguides, bending waveguide is a rather common structure. The customary technologies are only able to measure the bending loss of a single-mode waveguide, and total bending loss of a multi-mode waveguide. It is not capable of distinguishing the individual bending loss of every individual mode for a multi-mode waveguide. However, for multi-mode waveguide, the propagation loss and bending loss serve not only the evaluation function for improvement of manufacturing process, they are of considerable use in enhancing the designs of optical-components. They can also be applied in obtaining further understanding of multi-mode waveguide's individual mode function and physical behaviors.
Presently, the customary technologies used for measuring waveguide propagation loss include the following:
1.) Cut-back method as shown in FIG. 1 (I. P. Karminow & L. W Stulz, Loss in cleaved Ti-diffused LiNbO.sub.3 waveguides, Appl. Phys. Lett. 33, P. 62, 1978). PA1 2.) Prism-Sliding Method as shown in FIG. 2 (H. P. Weber, F. A. Dunn & W. N. Leibolt, Loss measurements in thin film optical waveguide, Appl. Opt. 12, 755, 1973) PA1 3.) Scattering-Detection Method as shown in FIG. 3 (J. E. Goell & R. D. Standley, Sputtered glass waveguide for integrated optical circuits, Bell Syst, Tech, J. 48, 3445, 1969) PA1 4.) Phase-Modulation Method as shown in FIG. 4 (L. G. Shen, C. T. Lee, H. C. Lee, Non-destructive measurement of loss performance in channel waveguide devices with phase modulator, Opt. Rev. 3, 192, 1996)
When the length of a waveguide is L.sub.1, the light is coupled into the edge of waveguide 1 through lens 2; the output light of the another edge of waveguide 1 is projected into optical-detector 4 through output Lens 3 for measuring optical intensity P.sub.1. The length of Waveguide 1 is then cleaved into a length of L.sub.2, and the light is projected into through the edge. The optical intensity measured is P.sub.2, and the propagation loss .alpha. is as follows: ##EQU1##
The disadvantage of this method is that, in addition to the destructive detection through cleaving waveguide, when couple light is introduced into the waveguide, the coupling efficacy each time must be the same, which is very difficult.
This method uses prism coupling method to couple light into Waveguide 1 through Prism 5, and the light comes out through Prism 6. Move the position of Prism 6; then use Optical Detector 4 to measure the outs of optical power of Prism 6 put at different positions. The values are compared to derive the waveguide's propagation loss. The drawback of this method is that coupling efficacy between prism and waveguide must be the same for different prism positions which is also exceedingly difficult.
With this method, Input Prism 5 is used to couple light to Waveguide 1, using Optic-Fibre 7 to capture the scattered light intensity of Waveguide 1 at different positions. Optic-Detector 4 is then used to measure the scattered optical power at different positions in deriving the propagation loss of waveguide. The drawback of this method is that it is only capable of measuring waveguides that scattered large optical power which must be avoided in integrated optical components.
This method is created by the applicant. Light is coupled at the edge of Waveguide 1 through Input Lens 2. Voltage is then applied to the phase modulator built by Electrode 8 for controlling the effective length of Waveguide 1 in forming Fabry-Perot etalon. Optic-Detector 4 is used for measuring, and osilloscope 9 shows the measured oscillation results for deriving it's associated contrast C, which is defined as C=(Imax-Imin)/(Imax+Imin). In which, Imax and Imin are the maximum and minimum values of the measured oscillation results. From the contrast value, the propagation loss .alpha. of Waveguide 1, when the length is L, is given by ##EQU2##
In which, R is the reflection coefficient at waveguide edge.